Vehicle emissions legislation prescribes certain limits for the emission of noxious gases in the exhaust stream of an internal combustion engine. Typically a catalytic converter is provided in the vehicle exhaust system, and operates to chemically convert noxious gases to relatively benign alternatives.
A catalytic converter requires a minimum temperature for effective operation, and this is achieved in a short period by heat transfer from the hot exhaust stream. When a vehicle starts in relatively cold conditions, the effective operation of the catalytic converter may be delayed. It would be desirable to reduce this delay so as to minimize emissions of untreated exhaust gas upon cold start.